How to claim or delete accounts after taking ownership of an abandoned domain?

[ehrenstein]

For my emerging business, I have just acquired a domain.

Now that I verified my ownership of the domain, I can see that there are 22 abandoned Atlassian accounts which have last been used three years ago, which 1) impedes my efforts to register new accounts and 2) may pose a security risk.

How can I remove those abandoned accounts from my domain?